It is a well known practice to place telecommunication cable innerduct in conduit to protect the cable. Typically, the conduit is laid in place or an innerduct is placed within the conduit and the cable is pulled therethrough. The innerduct serves as a guide and protector for the fragile telecommunications cable. To reduce the friction encountered during the pulling operation, various methods of lining the interior of the innerduct have been attempted. Heretofore, a significant limitation of reducing the friction involved in pulling a telecommunication cable through an innerduct has been the economy and efficiency of lining the innerduct with a proper low friction, lubricous material.
Innerducts and some conduits are typically polymeric tubes manufactured by coextruding a thermoplastic polymer with a line or rope placed therein. This rope is subsequently used to pull the telecommunication cable through the innerduct or conduit. Considering that the innerduct or conduit may be manufactured in lengths of 5000 feet, the process of pulling the telecommunication cable can be quite difficult and potentially damaging to the cable itself if significant friction is encountered between the inner surface of the innerduct and the cable.
One method used to reduce the friction is to texture the inner surface in order to reduce contact points between the cable and inner surface and, thus, the overall friction. However, this method is limited by the intrinsic properties of the innerduct or conduit material, by the material's ability to accept a texture, and by the physical distortion of the texture caused during the cable pulling process.
Another method involves lining the innerduct with a low friction, lubricous liner which is coextended with the innerduct, see for example U.S. Pat. No. 4,892,442. This method has the disadvantage that the coextrusion processes create unnecessarily thick liners. These liners are much thicker than the one-time cable pulling operation requires. Moreover, coextrusion is an inefficient way of lining shorter lengths of innerduct or conduit. The process is significantly inefficient in energy use since it involves melting a significant amount of the liner material prior to `thick cross section` application.
Another method involves the application of lubrication agents to the inner surface of the innerduct or conduits. This solution, however, is ineffective as well as troublesome since, during the pulling process, initial sections of the pulled-through cable tends to remove lubricating material for subsequent sections of the cable. The removal of the lubrication results in an increasing frictional gradient through the innerduct causing a potentially damaging stress gradient in the telecommunications cable. Furthermore, the use of lubricating materials to reduce the friction has a tendency to contaminate the telecommunications cable.
Accordingly, it is an object of this invention to overcome the limitations of the prior art methods and provide a method of lining an innerduct with a thin lubricous material which exhibits properties of low friction and ability to be textured in order to aid in the placement and reduce the pull-through force required to install telecommunications cable. It is also an object of the present invention to provide an innerduct having an inner surface with a low coefficient of friction to facilitate pull-through of the cables. It is yet another object of this invention to provide a method of lining a duct with exceptionally thin lining material which will serve to reduce friction for the anticipated single pull-through process while simultaneously providing a material and energy efficient lining method. It is another object of this invention to provide an innerduct liner which may be compounded with materials known for their low friction properties. It is another object of this invention to provide an innerduct liner which is homogeneous such that surface wear of the liner will not result in exposure of a material displaying increased frictional properties. It is another object of this invention to allow a thin liner material to be deposited with a textured surface in order to reduce surface contact with a telecommunication cable and thus decreased friction during pull-through. It is another object of this invention to produce an innerduct liner by hot melt deposition of a polymer or other friction reducing material to the inner surface of an innerduct. It is another object of this invention to provide a method of lining an innerduct or conduit which is adaptable to manufacture of both short and long lengths of innerduct or conduit. It is another object of this invention to provide a method of lining an innerduct or conduit which may easily be altered to provide a lining property variability along an innerduct or conduit length.